Between Arkham Origins and Assault on Arkham Incident
Assault on Arkham Incident
Arkham Asylum Incident
Zsasz threatened several doctors with the knife. If Batman was seen by Zsasz during these encounters, Zsasz will kill the doctor with the knife, automatically failing the encounter.
Arkham City Incident
One victim of Zsasz could be found leaning on a phone booth inside Arkham City, most likely killed with the knife. Another victim of his could be found floating in the water inside Zsasz's hideout, propably killed with the knife.